here's a little more translation of the map...sorry to use a french one, but it's the most recent i could find online...the most recent english-language map is from 2002. things have changed. at the bottom left, the map lists the principal mechanisms the israelis use to prevent palestinian movement around the west bank.
1) the settlements and the roads which are built or diverted to get to them all of which are completely forbidden to palestinians
2) 500-600 obstacles that cut up other roads--beyond the network of military checkpoints there roads are cut off with things like that puncture tires or with barricades. these are simply left in place, so the roads are impassable.
3) closed military zones
4) strictly controlled passes which are required to move south-to-north (or vice versa) across the west bank.
the only reason any of these controls exist is the settlements.
for example.
later: here's a larger-scale map from 2006 linked via wikipedia that's in english:
http://en.wikipedia.org/wiki/File:Westbankjan06.jpg
mostly for comparison's sake.
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one more addition:
here's a short web-piece that at least broaches the question of water access:
http://www.ifamericansknew.org/cur_sit/water.html
so the settlements are a big deal, but they're caught in other conflictual situations.
like water, who gets it, who does not.